1. Field of the Invention
This invention relates generally to surgically implanted physiological shunt systems and related flow control devices. More particularly, the present invention relates to a spring in a shunt system including a one-way flow control valve for controlling the flow of cerebrospinal fluid out of a brain ventricle and preventing backflow of fluid into the brain ventricle.
2. Description of Related Art
In the medical arts, to relieve undesirable accumulation of fluids it is frequently necessary to provide a means for draining a fluid from one part of the human body to another in a controlled manner. This is required, for example, in the treatment of hydrocephalus, an ailment usually afflicting infants or children where fluids accumulate within the skull and exert extreme pressure and skull deforming forces.
In treating hydrocephalus, cerebrospinal fluid accumulated in the brain ventricles is typically drained away utilizing a drainage or shunt system including a catheter inserted into the ventricle through the skull, which is connected to a tube that conducts the fluid away from the brain to be reintroduced into the peritoneal cavity or into the vascular system, as by extending a distal catheter through the patient""s jugular vein to the atrium portion of the heart.
To control the flow of cerebrospinal fluid and maintain the proper pressure in the brain ventricle, a pump or valve is placed in the conduit between the brain and the peritoneal cavity or the heart. An exemplary flow control device is found in U.S. Pat. No. 4,560,375.
Although such drainage systems have provided successful results, a problem of overdrainage of the cerebrospinal fluid from the brain ventricles sometimes exists. Overdrainage of cerebrospinal fluid may result in excessive reduction of the cerebrospinal fluid pressure within the brain ventricles and predispose the development of a subdural hematoma or hydroma, and excessive reduction of ventricular size leading to shunt obstruction because of impingement of the ventricular walls on the inlet holes of the ventricular catheter.
This overdrainage can be caused by the siphoning effect of hydrostatic pressure in the distal shunt catheter. The siphoning effect of hydrostatic pressure may be created by the elevation of the ventricular catheter inlet with respect to the distal catheter outlet (i.e., when the patient sits, stands or is held erect). In order to prevent such overdrainage caused by the siphoning effect of hydrostatic pressure in the distal shunt catheter, siphon control devices have been placed in the conduit, typically between the flow control device and the peritoneal cavity or the heart. An exemplary siphon control device is found in U.S. Pat. No. 4,795,437.
It is desirable in some instances to permit the physician to be able to alter the flow characteristics through the drainage system after it has been subcutaneously implanted. To this end, on-off devices have been provided for implantation as a portion of the fluid conduit as an additional element of the shunt. An exemplary on-off device is shown in U.S. Pat. No. 3,827,439. Moreover, flow control devices have been provided which utilize a plurality of flow control valves having different flow control characteristics, which provide, alternative fluid pathways therethrough such that selection of a desired fluid pathway can be made by the selective percutaneous manipulation of the device when subcutaneously implanted. Such flow control devices having selectable alternative fluid pathways are shown in U.S. Pat. Nos. 5,154,693 and 5,167,615, the contents of which are incorporated herein in their entireties by reference.
These prior fluid shunt devices have all shared one important limitation: they only permit fluid flow therethrough upon achieving at most two fluid pressure differentials at the inlet and outlet of the device. In treating hydrocephalus, however, it is often desirable to vary the device xe2x80x9copeningxe2x80x9d pressure differential in accordance with ventricle size and treatment objective. For example, initial treatment may require a lower than normal pressure differential to initiate shrinkage of the ventricles, but as the ventricles decrease in size, the pressure differential should be increased gradually so that when the ventricle is returned to normal size the intraventricular pressure is at its normal value and the intracranial force systems are in balance (i.e., the opening differential pressure is set at a level that will stabilize the ventricles at a desired size). Generally speaking, the opening differential pressure should be varied inversely with the ventricle size. It is desirable to leave a lower pressure valve in a patient after the ventricles are again normal size, because the ventricles can further collapse, leading to a condition known as xe2x80x9cslitxe2x80x9d ventricles.
A further reason for providing adjustability in the opening pressure differential is to correct for variations in nominal opening pressure differentials typical in manufactured valves. With an adjustable valve, the opening pressure differential can be more accurately set at the factory and can be checked and corrected if necessary in the operating room prior to implantation.
Accordingly, there was a need in the medical arts for convenient and effective physiological drainage systems for controlling the flow of fluid from one part of the body to another, which are relatively inexpensive to manufacture, permit fluid flow therethrough only when upstream fluid pressure exceeds downstream fluid pressure by a selected pressure differential, and also provide means for altering the selected pressure differential by percutaneous manipulation of the device when it is subcutaneously implanted. Moreover, such a flow control device was needed that incorporates an integral siphon control device that opens only in response to positive upstream fluid pressure, and re-closes or remains closed in the absence of such positive upstream fluid pressure or in response to negative downstream hydrostatic pressure on the device.
These objectives were met in the invention described in U.S. Pat. No. 5,637,083, issued Jun. 10, 1997 to William J. Bertrand and David A. Watson entitled xe2x80x9cIMPLANTABLE ADJUSTABLE FLUID FLOW CONTROL VALVExe2x80x9d, assigned to the assignee of the present invention, the contents of which are incorporated herein in its entirety. The invention described in the ""083 patent resides in an improved subcutaneously implantable and percutaneously adjustable fluid flow control device useful in a physiological shunt system for controlling the flow of fluid from one part of the body to another. The fluid flow control device includes components responsive to an external or percutaneously-applied magnetic field, to provide the device a variety of pressure/flow characteristics.
In accordance with the invention described in the ""083 patent, the fluid flow control device comprises an inlet, an outlet and valve means for controlling the fluid flow from the inlet to the outlet. The valve means comprises a valve housing including a fluid passageway therethrough that has a peripheral surface that forms a valve seat, and a valve element having a diameter larger than the valve seat. Means are provided for biasing the valve element against the valve seat so as to keep the fluid passageway closed until a fluid pressure differential between the inlet and the outlet exceeds a selected valve opening pressure. Further, a pump is situated between the inlet and the valve means. The pump provides means for flushing fluid through the device by the application of percutaneous pressure to the pump.
In one preferred form of the invention of the ""083 patent, the valve housing includes a threaded aperture and a flow regulator insert which is threaded into the aperture to define the fluid passageway. Means are provided for adjusting the amount of bias applied to the valve element by the biasing means. In particular, the adjusting means includes a fixed dual concentric stair-step array and an overlying rotor assembly having a first surface which supports an end of a valve element-biasing spring, and a second surface which is supported by the stair-step array. The rotor assembly is adapted to rotate in response to an external or percutaneously-applied magnetic field and such rotation of the rotor assembly permits selected seating of the second surface on the stair-step array to raise or lower the rotor assembly with respect to the stair-step array.
The dual concentric stair-step array includes a central rotor pivot, a plurality of inner steps surrounding the rotor pivot, and a plurality of outer steps extending peripherally about the inner steps. The rotor assembly includes a magnet embedded within a base having an inner leg adapted to bear against a selected one of the plurality of inner steps, and outer leg disposed diametrically opposite the inner leg and adapted to bear against a selected one of the plurality of outer steps, a central aperture through which the rotor pivot extends, and a rotor cap fixed to the base on a side thereof opposite the inner and outer legs. The rotor cap provides the first surface of the rotor assembly and includes a central aperture aligned with the central aperture of the base, through which the rotor pivot extends.
A compression spring is provided between a portion of the valve housing surrounding the fluid passageway and the first surface of the rotor assembly. The compression spring biases the rotor assembly into contract with the dual concentric stair-step array.
Means are also provided for occluding a portion of the fluid flow control device adjacent to the inlet by application of manual percutaneous pressure to the device. Similarly, means are provided for occluding a portion of the fluid flow control device adjacent to the outlet also by application of manual percutaneous pressure to the device.
Moreover, a siphon control device is situated between the valve and the outlet.
In another preferred form of the invention of the ""083 patent, means are provided for locking the rotor assembly into one of several possible rotational positions relative to the stair-step array to prevent rotation thereof Further, means are provided for disengaging the locking means to permit rotation of the rotor assembly in response to the external magnetic field. More particularly, the locking means comprises a pin having a first end that engages one of a plurality of detents in an outer peripheral surface of the rotor assembly to prevent rotation thereof.
The disengaging means comprises pin-actuating means for moving the pin between a first extended position, wherein the end of the pin engages one of the plurality of detents, and a second retracted position. The pin actuating means comprises a pivotable lever including a pin-engaging shaft that engages a second end of the pin, and a manually actuated lever disposed within the pump and biased so as to urge the pin into its first position.
A spring and a method of making a spring are described. The spring is made by etching or cutting at least one, but preferably two or more interleaved arms in a flat substrate leaving intermediate residual material between the arms or around the arm where there is only a single arm. The intermediate residual material is either pushed or lifted to form a conical spring.
It is an object of the present invention in one embodiment to provide a spring that has a linear compression versus spring constant range.
It is an object of the present invention in one embodiment to provide a spring that is substantially flat when fully compressed.
It is an object of the present invention in one embodiment to provide a method of making springs that allows several springs to be made concurrently.
It is an object of the present invention in one embodiment to provide a method of making springs that allows several springs to be made precisely.
It is an object of the present invention in one embodiment to provide a method of making springs that allows several springs to be made economically.
It is an object of the present invention in one embodiment to provide a method of making springs that allows several springs to be made reproducibility.
Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.